Ghostbusters: The eponymous busters have to Cross The Streams to do it, but they defeat Gozer the Gozarian, an ancient god worshipped by the Hittites, Mesopotamians, and the Sumerians around 6000BC that would take on a Destructor Form from the thoughts of humans in the area and wreak havoc once it was summoned into our world.
"We came, we saw, we kicked its ass"!
Conan the Destroyer: what to do when you involuntarily helped the return of an ancient monstrous god? Wrestle him and rip his horn with bare hands, of course!
In Dogma, when Silent Bob kills the demon Azrael with Cardinal Glick's driver. Granted, the clubs in question were blessed by a priest (because the priest would be the kind of guy to do that), but when mortals are taking out demons you can't be picky about the methodology..
Subverted in Sin City where this very act is invoked (sarcastically) as a metaphor for doing something that is completely impossible.
Hartigan: And after I pull off that miracle, maybe I'll go punch out God.
In The Avengers, Loki taunts pretty much every hero he speaks to, and at minimum holds his own in direct combat. Near the end of the final battle, Loki comes face-to-face with the Incredible Hulk, and starts taunting him as before. He's barely gotten 3 sentences out when Hulk grabs him and starts thrashing him around the room like a ragdoll, knocking him silly and taking him out of the fight. And ends with the phrase, "Puny God."
In Independence Day, Will Smith's character punched out a alien pilot. May be a bit of a stretch, but the Aliens were snuffing out humanity's armies with relative ease at this point. (Also of note, the alien had tentacles in place of arms and hands, though it otherwise did not resemble a Cthulhu.)
Hellboy features its titular demonic hero being swallowed by the tentacled God of Chaos. Fortunately Hellboy was wearing a belt of grenades which he then detonated, blowing the creature up from the inside, leaving Hellboy remarkably unharmed.
